Science is an investigation into nature and the operations of the universe that proceeds by testing explanatory theories against empirical evidence. This process is called the scientific method. Scientists have long recognized that evolution accounts for the diversity of life on earth. Using the methods of scientific inquiry and analysis, biologists have established that human beings and other species evolved over time through processes including natural selection. It is entirely appropriate, therefore, for public schools to make evolution a significant part of their biology curricula.

Although the role of evolution in shaping the biological world is accepted as a fact in the scientific community, some religious people – from a variety of faiths – reject its veracity because they believe that it is irreconcilable with divine explanations of creation.

In their view, the teaching of evolution in public schools represents an anti-religious bias against Christians, Jews, and others who believe in supernatural creation. Many opponents of the teaching of evolution believe that it is merely one example of the "secular-humanist" religion that government favors in place of traditional Judeo-Christian beliefs. Demanding a much higher level of proof for evolution’s claims than other widely accepted scientific theories, they argue that evolution remains unproven and that schools should give equal time to creationism, creation science or intelligent design.